The invention relates to a method for operating a hybrid drive device of a motor vehicle, wherein the hybrid drive device has an internal combustion engine which can be operatively coupled with a first axle of the motor vehicle, a first electric motor which can also be operatively coupled with the first axle, and a second electric motor which can be operatively coupled with a second axle of the motor vehicle. The invention also relates to a hybrid drive device of a motor vehicle and a corresponding motor vehicle.
The hybrid drive device serves for driving the motor vehicle and for this purpose has multiple drive aggregates, of which at least two are of a different type. One of the drive aggregates is for example constructed as an internal combustion engine, while the first electric motor and the second electric motor represent further ones of the drive aggregates. The motor vehicle has at least two axles, i.e., the first axle and the second axle. The internal combustion engine and the first electric motor can be or are operatively connected with the first axle. For example, a separating clutch is present in the operative connection between the first axle and the internal combustion engine, so that the operative connection can be at least temporarily interrupted. The first electric motor is preferably permanently operatively connected with the first axle. As an alternative, however, also in this case a separating clutch can be provided in the operative connection between the first electric motor and the first axle of the motor vehicle. The second electric motor can be or is operatively connected with the second axle of the motor vehicle. Preferably, as described above for the first electric motor, this is permanently the case. However, as an alternative, a separating clutch can also be provided in this case between the second electric motor and the second axle.
The motor vehicle has thus at least two drivable axles, because the first axle can be driven with the internal combustion engine, the first electric motor or with both the internal combustion engine and the electric motor. The second axle on the other hand can be driven by means of the second electric motor. The term “driving” means in this context providing a torque of any direction at the respective axle. The torque can thus be directed to an acceleration as well as deceleration of the motor vehicle. Particularly preferably, the first axle and the second axle are the only axles of the motor vehicle; the motor vehicle thus only has the first axle and the second axle. Correspondingly the motor vehicle can be operated at least temporarily as all-wheel-drive vehicle.
Such a drive device enables in a simple manner selectively driving only the first axle, only the second axle or the second axle and the first axle. However, because the first axle of the motor vehicle can be operatively connected with the internal combustion engine, it is referred to as primary axle, while the second axle represents a secondary axle. Preferably the second axle is only driven by means of the second electric motor when at the same time the first axle is also driven with the internal combustion engine and/or the first electric motor. It can thus be provided that the second electric motor is only operated for driving the second axle when also the internal combustion engine, the first electric motor or both are operated, i.e., serve for providing a torque which acts on the first axle. The hybrid drive device serves for realizing the advantages of a single axle drive, i.e., in which only the first axle is driven, as well as a multiple axle drive, in which the first axle as well as the second axle of the motor vehicle are driven. However, the multiple axle drive adversely effects fuel consumption of the hybrid drive device and thus the vehicle.
From the state of the art the printed publication DE 10 2011 078 498 A1 is known. This document describes a method for operating a drive train of a vehicle, which includes driving first wheels by using an electric motor, starting a machine, using a second electric motor driven by the machine in order to generate a synchronous rotational speed at the input of the transmission with a desired set gear, engaging a clutch, which connects the input and the machine, and using the machine and the transmission in order to drive second wheels. Also the printed publications US 2006/0173593 A1, DE 10 2007 046 584 A1 and DE 10 2005 048 501 B3 are known from the state of the art.